This invention relates to methods of reducing the deposition of organic contaminants, such as pitch and stickies, in papermaking processes. The deposition of organic contaminants on process equipment, screens, and containment vessels in papermaking can significantly reduce process efficiency and paper quality. Deposits on machine wires, felts, foils, headbox surfaces, screens, and instruments can result in costly downtime for cleaning to avoid the problems associated with poor process control, reduced throughput, and substandard sheet properties. Such contaminants are generically referred to in the paper industry as either “pitch” or “stickies”. Pitch deposits generally originate from natural resins present in virgin pulp, including terpene hydrocarbons, rosin/fatty acids or salts thereof, such as pimaric acid, pinic acid and abietic acid, glyceryl esters of fatty acid, sterols, etc. Stickies and white pitch generally refer to the hydrophobic substances used in the manufacture of paper such as sizing agents, coating binders, and pressure sensitive or contact adhesives. Such substances can form deposits when reintroduced in recycled fiber systems. Other common organic contaminants that are chemically similar to stickies and found in recycle applications include wax, which originates primarily from wax-coated old corrugated containers, and polyisoprene. Pitch and stickies may also contain entrapped inorganic materials such as talc, calcium carbonate, or titanium dioxide.
Recycled fiber also refers to secondary fibers which are repulped to provide the papermaking furnish with raw material for the production of new papers. The secondary fibers may be either pre-consumer or post-consumer paper material that is suitable for use in the production of paper products. Sources of secondary fiber may include old newspaper (ONP), old corrugated containers (OCC), mixed office waste (MOW), computer printout (CPO), ledger, etc. These once-processed papers contain various types of adhesives (pressure sensitive, hot melts, etc.), inks, and coating binders.
Pitch and stickies are hydrophobic in nature and thus unstable as colloids in aqueous papermaking environments, thereby facilitating their deposition. The major problems arising from deposition are as follows: (1) reduced throughput due to plugging of forming fabrics and press felts, (2) sheet holes or paper breaks due to large deposits breaking loose from the equipment, and (3) reduced sheet quality due to large particle contaminants incorporated in the final sheet.
One approach used to address pitch and stickies deposition is through the use of detackifiers. Detackifiers passivate the exposed surfaces of pitch and sticky particles rendering them non-adhesive and unlikely to deposit. A number of chemical are known to be effective detackifiers. Effective organic detackifiers include polyvinyl alcohol, copolymer of vinyl alcohol and vinyl acetate, polyethylene oxide, polyacrylates, and waterborne globulins. In order for detackifiers to function well, it must satisfy two crucial functions: 1) it must selectively and sufficiently attach to the surface of the pitch or sticky surface, and 2) it must stabilize the resulting sticky/pitch-detackifier complex in water.
The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is “Prior Art” with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 CFR §1.56(a) exists.